When you are in the business of popular music you look for indications of success that aren't susceptible to manipulation. For example, Facebook friends and Twitter followers can be faked, Last FM total plays and users can't. Spotify plays can not.
One indicator which is just brutally, brutally honest is ticket pre-sales. Man, there is no denying what ticket pre-sales tell you about the comparative popularity of two Artists. It's only within the past six months that I've had access to both national and local pre sale figures and.....it really poses existential questions. Sure, walk up is great, and sell outs based on walk up is great, but it is a big difference between doing that and selling out a month in advance. And it is great if you sell out a 200-300 person venue, but let's be honest... you are probably treading water unless you can sell 10x that number of tickets.
But I now have access to local pre sale tickets in both San Diego and Los Angeles, and access to national and international pre-sales, and then I kind of keep track of sell outs in other markets and the size of venues and man the news is just always brutal. It's also truth about the real popularity of a specific Artist.